It is well known in the art that the NH-group of the indole nucleus of the amino acid tryptophan is liable to an attack of several reagents if said NH-group is present as free, not protected NH-group. The problems are specially severe if the synthesis of a dipeptide, polypeptide or protein has to be performed which comprises in its amino acid sequence at least one moiety of tryptophan and furthermore at least one moiety of arginine which has its guanidino group protected. Even if the guanidino-protecting group is split off using extremely mild conditions, the yields of the corresponding dipeptide, polypeptide or protein are lowered due to an attack at the NH-group of the indole nucleus of the tryptophan.
Until now several protective groups for the NH of the indole nucleus of tryptophan in combination with several protective groups for the alphaamino group of tryptophan were used in order to avoid the above stated difficulties. However, until now no combination of protective groups for the indole nucleus with protective groups for the alphaamino groups were found out which on the one hand result in corresponding protected derivatives which have the necessary stability and which can be used for the performance of the synthesis of dipeptides, polypeptides and proteins in which synthesis no drastical lowerings of the yield are observed in the reaction step where sidechain protective groups of other amino acids of the amino acids sequence are split off.
It was the aim of the present invention to provide new protected derivatives of tryptophan which do not have the disadvantages of the until now used protected derivatives.